While it has always been important, air pollution has become an even greater concern today. Not only is there concern over the air pollutants emitted by industrial processes and electric power generating stations, there is also increasing concern over the deliberate pollution of the atmosphere by terrorist groups with toxic or radioactive pollutants. Thus, more than ever it is necessary to have quick and easy methods of collecting and identifying air pollutants and to determine the location from which such particles are emitted.
Accordingly, it is a general object of the present invention to provide a method and apparatus for rapidly and easily extracting pollutants from the air for analysis and identification.
Today, there are many state, federal, and municipal regulations relating to the permissible level of particulate matter that can be emitted in industrial processes and reliable, inexpensive means are needed to determine if the regulatory requirements are being met.
Accordingly, it is another object of the present invention to provide a means and method for the determination of the level of undesirable particulate matter at various locations and altitudes, and at various times.
In the prior art, probably the most commonly employed method for measuring particulate matter in the air has been to force air samples to flow through a filter or a series of filters after which the filters are weighed and analyzed for the presence of particulate matter. However, significant pumping power is required to force air through filters and while this can be done on a stationary basis, the amount of power required for sampling for extended periods of time makes it impractical to use filters in a portable detector. Accordingly, it is another object of this invention to provide a particulate matter extractor which can be operated for relatively long periods of time with very low energy consumption. Furthermore, not only is it difficult and expensive to separate particles from a filter, filters are size sensitive as very small particles will pass through with only larger ones being entrapped in the filter.
As an alternative to filters, use has been made of electrostatic precipitators to collect particles. One of these prior art devices is described in U.S. Pat. No. 2,868,318, which issued on Jan. 13, 1959 to W. A. Perkins, et al. In the Perkins' device a coronal glow discharge in air around a cathode is established and particles charged thereby are collected on an anode spaced at some distance from the cathode. However, it appears that this precipitator device must be disassembled and the anode removed to analyze samples. Accordingly, it is another object of the present invention to provide a method and apparatus whereby the extractor does not require extensive dismantling in order to recover the collected particulate matter for analysis.
In another prior art device, electrostatic precipitation is employed to determine the mass of particulate matter entrained in a gaseous flow per unit volume. This device is described in U.S. Pat. No. 3,718,029 which issued on Feb. 27, 1973 to Gourdine et al. In this patent, the dust particles in the air are charged by an electric field and are subsequently collected on a dielectric surface positioned in front of the grounded electrode. The amount of accumulated charge on the dielectric surface is subsequently measured by an induction electrode to determine the particulate mass per unit volume of the air flow. In this patent, a quantitative method of determining particulate matter is disclosed but no means is provided to remove the particles for qualitative analysis. Accordingly, it is another object of the present invention to provide a method and means for qualitative determination of the make up of the particulate matter collected from air.
Yet another electrostatic precipitator is described in U.S. Pat. No. 3,879,986 which issued on Apr. 29, 1975 to George A. Schmel. In this device electrostatic precipitation onto a grid is accomplished with the use of a coronal glow discharge to charge the particles. The electrode in this case is shaped and spaced so as to allow the precipitation of particles in a controlled manner. A point electrode and a grid are used in a combination which separates particles by size. However, another object of the present invention is to provide precipitation for all charged particulate matter and not to selectively collect or precipitate particles.
Still another object of the invention is to provide a method and means for collecting aerosols for pre-determined intervals of time at selected locations.
The foregoing and other objects are achieved by the present invention which is described in the Summary of the Invention and Detailed Description and drawings which follow.